Wound cleansing apparatus in-situ

ABSTRACT

An apparatus for cleansing wounds, in which wound exudate is removed from a wound bed and selectively cleansed and returned to the wound. The cleansing means removes materials deleterious to wound healing, and the cleansed fluid, still containing materials that are beneficial in promoting wound healing, is returned to the wound bed. The associated wound dressing and cleansing means are conformable to the wound, and may have irrigant fluid circulated from a reservoir by a device for moving fluid through a flow path which passes through the dressing and a means for fluid cleansing and back to the dressing.

The present invention relates to apparatus and a medical wound dressingfor cleansing wounds, and a method of treating wounds using suchapparatus.

It relates in particular to such an apparatus, wound dressing and methodthat can be easily applied to a wide variety of, but in particularchronic, wounds, to cleanse them of materials that are deleterious towound healing, whilst retaining materials that are beneficial inparticular to wound healing.

Before the present invention, aspirating and/or irrigating apparatuswere known, and tended to be used to remove wound exudate during woundtherapy. In known forms of such wound therapy, the offtake from thewound, especially when in a highly exuding state, is voided to waste,e.g. to a collection bag.

Materials deleterious to wound healing are removed in this way. However,materials that are beneficial in promoting wound healing, such as growthfactors, cell matrix components, and other physiologically activecomponents of the exudate from a wound are lost to the site where theycan be potentially of most benefit, i.e. the wound bed, when suchtherapy is applied.

Such known forms of wound dressing and aspiration and/or irrigationtherapy systems thus often create a wound environment under the dressingthat may result in the loss of optimum performance of the body's owntissue healing processes and in slow healing, and/or in weak new tissuegrowth that does not have a strong three-dimensional structure adheringwell to and growing from the wound bed. This is a significantdisadvantage, in particular in chronic wounds.

It thus would be desirable to provide a system of therapy which

-   a) can remove materials deleterious to wound healing from wound    exudate, whilst-   a) retaining materials that are beneficial in promoting wound    healing in contact with the wound bed.

Dialysis is a known method of treating bodily fluids such as blood exvivo, to cleanse them of materials that are deleterious to the bodysystemically. Removal of such materials by contact with the dialysate isthe prime purpose of dialysis, whilst also retaining materials such asblood, cells and proteins. Other materials that may have an additionalpositive therapeutic action are potentially lost to the system throughthe dialysis membrane, which is also permeable to them. The balance ofsuch materials in the bodily fluid in recirculation may thus be furtherdepleted.

It would be desirable to provide a system of therapy that can removematerials deleterious to wound healing from wound exudate, withoutsubstantially diluting materials that are beneficial in promoting woundhealing in contact with the wound bed, and which can continuously supplyand recirculate such materials to the wound simultaneously.

Dialysis for treating bodily fluids is also a systemic therapy, sincethe treated fluid is returned to within the body. This is in contrast toa topical therapy in which the treated fluid is recycled outside thebody, e.g. to a wound.

Dialysis also requires large amounts either of bodily fluids, such asblood, or dialysate, and consequently the relevant devices tend not tobe portable. Even when in a highly exuding state, chronic wounds producerelatively little fluid to be treated compared with internal bodilysystems and relatively little materials that are beneficial in sometherapeutic aspect to be retained in the wound and/or its environment.

It is an object of the present invention

-   a) to obviate at least some of the abovementioned disadvantages of    known aspiration and/or irrigation therapy systems, and-   b) to provide a system of therapy which can    -   i) remove materials deleterious to wound healing from wound        exudate, whilst    -   ii) retaining materials that are beneficial in promoting wound        healing in contact with the wound bed.

It is a further object of the present invention

-   a) to obviate at least some of the abovementioned disadvantages of    known dialysis systems, and-   b) to provide a system of therapy which can remove materials    deleterious to wound healing from wound exudate, whilst retaining    materials that are beneficial in promoting wound healing in contact    with the wound bed,-   c) without affecting the body systemically.

It is a yet further object of the present invention

-   a) to obviate at least some of the abovementioned disadvantages of    known dialysis systems, and-   b) to provide a system of therapy which can remove materials    deleterious to wound healing from wound exudate, whilst retaining    materials that are beneficial in promoting wound healing in contact    with the wound bed, and-   c) is portable.

Vascular supply to, and circulation in, tissue underlying andsurrounding the wound is often compromised. It is a further object ofthe present invention to provide a system of therapy that retains andsupplies therapeutically active amounts of materials that are beneficialin reversing this effect whilst removing deleterious materials, therebypromoting wound healing.

Thus, according to a first aspect of the present invention there isprovided an apparatus for cleansing wounds, comprising

a conformable wound dressing, havinga backing layer which is capable of forming a relatively fluid-tightseal or closure over a wound andcharacterised in that it also comprises

-   a) a cleansing means for selectively removing materials that are    deleterious to wound healing from wound exudate, which means is    under the backing layer and sits in the underlying wound in use and-   b) a moving device for moving fluid through the cleansing means, and-   c) optionally bleed means for bleeding the cleansing means.

The term ‘bleed means for bleeding the cleansing means’ includes anybleed means that is in fluidic communication with the cleansing means.

Materials deleterious to wound healing are removed by the cleansingmeans, and the cleansed fluid remains in and/or is returned to thewound.

The fluid thus retains naturally occurring materials in the woundexudate that are potentially beneficial to wound healing intherapeutically active amounts

The apparatus for cleansing wounds of this first aspect of the presentinvention is based on this principle: by moving fluid through thecleansing means, the moving device continually brings materials that aredeleterious to wound healing and the cleansing means into mutual dynamiccontact, rather than relying on the passive movement of such materials,e.g. by diffusion under a chemical potential gradient in a fluid. Theirremoval from the wound exudate occurs more rapidly with such fluidmovement.

There are various embodiments of the apparatus of the first aspect ofthe present invention for different types of application, including inparticular those that are described in detail hereinafter. No matter howdifferent they may be, it is believed that they may be classified intothe following functional types, typified by which fluid passes throughthe cleansing means:

1. A ‘Single-Phase System’

-   -   In this, the fluid that is moved through the means for fluid        cleansing is wound exudate optionally mixed with an irrigant.        This passes into, through and out of the cleansing means, e.g. a        chamber under the backing layer, and back to the wound bed.        Materials deleterious to wound healing pass into and are removed        by the means for fluid cleansing before return of the cleansed        fluid to the wound bed.

2. A ‘Multiple-Phase System’

-   -   In this, the wound exudate remains in the wound, and does not        pass into the cleansing means on a macro-scale. The means for        fluid cleansing often comprises a chamber containing a second,        cleansing fluid, most usually a fluid (dialysate) phase. The        latter is separated from the wound exudate by means of a        permeable integer, for example often a polymer film, sheet or        membrane. The fluid that is moved through the means for fluid        cleansing by the device for moving fluid is the cleansing fluid        and/or the wound exudate optionally mixed with irrigant.

In both single- and multiple-phase systems, it may be appropriate todesign and run the device to move fluid through the wound or thecleansing means to operate the system as a ‘circulating system’.

In this, the relevant fluid passes through the cleansing means one ormore times in only one direction.

Alternatively, where appropriate it may be provided in the form of a‘reversing system’. That is, the relevant fluid passes through thecleansing means at least once in opposing directions.

The apparatus of the first aspect of the present invention may howeverin different types of application be operated both as a circulatingsystem and as a reversing system, in which the relevant fluid passesthrough the cleansing means at least once in the same and in opposingdirections. (See FIG. 2 hereinafter).

The type of cleansing means may determine the appropriate design andmode of running the present apparatus.

The cleansing means may as desired be operated as a ‘single-passsystem’, i.e. the relevant fluid passes through the cleansing means onlyonce.

Alternatively, where appropriate it may be provided in the form of a‘multiple-pass system’, in which the relevant fluid passes through thecleansing means and/or over the wound bed several times.

It will be seen that the combination of these parameters create a numberof main embodiments of the present invention. In summary, these are:

1. A ‘Single-Phase System’

-   -   a) as a ‘circulating system’, in which the wound exudate and        optionally irrigant passes through the cleansing means one or        more times in only one direction (Examples of such a system are        shown in FIGS. 2, 4, 8, 9, 11 and 15 hereinafter.), or    -   b) as a ‘reversing system’, i.e. the wound exudate and        optionally irrigant passes through the cleansing means at least        once in opposing directions. (Examples of such a system are        shown in FIGS. 1, 2, 3, 6, 7, 10 and 14 hereinafter.)    -   This type of cleansing may be operated as a    -   i) ‘single-pass system’, i.e. the relevant fluid passes through        the cleansing means only once, or    -   ii) as ‘multiple-pass system’, in which the relevant fluid        passes through the cleansing means and/or over the wound bed        several times.

2. A ‘Multiple-Phase System’

-   -   a) as a ‘circulating system’, in which        -   (i) the wound exudate and optionally irrigant and/or        -   (ii) a cleansing fluid        -   each passes through the cleansing means one or more times in            only one direction (Examples of such a system are shown in            FIGS. 12 and 13 hereinafter.), or    -   b) as a ‘reversing system’, i.e.        -   (i) the wound exudate and optionally irrigant and/or        -   (ii) a cleansing fluid        -   each passes through the cleansing means at least once in            opposing directions.    -   This type of cleansing may be operated as a    -   i) ‘single-pass system’, i.e. the relevant fluid passes through        the cleansing means only once, or    -   ii) as ‘multiple-pass system’, in which the relevant fluid        passes through the cleansing means and/or over the wound bed        several times.    -   In such a ‘multiple-phase system’, where both the cleansing        fluid and/or the wound exudate optionally mixed with irrigant        are moving, the flows may be cocurrent or countercurrent,        preferably countercurrent    -   Examples of such circulating systems are shown in:    -   FIGS. 12 a and 13 in which the exudate is static and a cleansing        fluid passes through the cleansing means one or more times in        only one direction, and    -   FIG. 12 b, in which the exudate and optionally irrigant and a        cleansing fluid each pass through the cleansing means one or        more times in only one direction, here countercurrent to each        other.

The general features of the dressing of the present invention will nowbe described, followed by specific features related to specificcleansing means within the dressing.

In all embodiments of the apparatus of this first aspect of the presentinvention for cleansing wounds, a particular advantage is the tendencyof the wound dressing to conform to the shape of the bodily part towhich it is applied.

The wound dressing comprises a backing layer with a wound-facing facewhich is capable of forming a relatively fluid-tight seal or closureover a wound.

The term ‘relatively fluid-tight seal or closure’ is used herein toindicate one which is fluid- and microbe-impermeable and permits apositive or negative pressure of up to 50% atm., more usually up to 15%atm. to be applied to the wound. The term ‘fluid’ is used herein toinclude gels, e.g. thick exudate, liquids, e.g. water, and gases, suchas air, nitrogen, etc.

The shape of the backing layer that is applied may be any that isappropriate to aspirating, irrigating and/or cleansing the wound acrossthe area of the wound.

Examples of such include a substantially flat film, sheet or membrane,or a bag, chamber, pouch or other structure of the backing layer, e.g.of polymer film, which can contain the necessary fluids.

The backing layer may be a film, sheet or membrane, often with a(generally uniform) thickness of up to 100 micron, preferably up to 50micron, more preferably up to 25 micron, and of 10 micron minimumthickness.

Its largest cross-dimension may be up to 500 mm (for example for largetorso wounds), up to 100 mm (for example for axillary and inguinalwounds), and up to 200 mm for limb wounds (for example for chronicwounds, such as venous leg ulcers and diabetic foot ulcers.

Desirably the dressing is resiliently deformable, since this may resultin increased patient comfort, and lessen the risk of inflammation of awound.

Suitable materials for it include synthetic polymeric materials that donot absorb aqueous fluids, such as

polyolefins, such as polyethylene e.g. high-density polyethylene,polypropylene, copolymers thereof, for example with vinyl acetate andpolyvinyl alcohol, and mixtures thereof;polysiloxanes;polyesters, such as polycarbonates;polyamides, e.g. 6-6 and 6-10, andhydrophobic polyurethanes.

They may be hydrophilic, and thus also include hydrophilicpolyurethanes.

They also include thermoplastic elastomers and elastomer blends, forexample copolymers, such as ethyl vinyl acetate, optionally or asnecessary blended with high-impact polystyrene.

They further include elastomeric polyurethane, particularly polyurethaneformed by solution casting.

Preferred materials for the present wound dressing include thermoplasticelastomers and curable systems.

The backing layer is capable of forming a relatively fluid-tight seal orclosure over the wound and/or around the inlet and outlet pipe(s).

However, in particular around the periphery of the wound dressing,outside the relatively fluid-tight seal, it is preferably of a materialthat has a high moisture vapour permeability, to prevent maceration ofthe skin around the wound. It may also be a switchable material that hasa higher moisture vapour permeability when in contact with liquids, e.g.water, blood or wound exudate. This may, e.g. be a material that is usedin Smith & Nephew's Allevyn™, IV3000™ and OpSite™ dressings.

The periphery of the wound-facing face of the backing layer may bear anadhesive film, for example, to attach it to the skin around the wound.

This may, e.g. be a pressure-sensitive adhesive, if that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound-facing face of the wound dressing.

Alternatively or additionally, where appropriate a light switchableadhesive could be used to secure the dressing in place to preventleakage. (A light switchable adhesive is one the adhesion of which isreduced by photocuring. Its use can be beneficial in reducing the traumaof removal of the dressing.)

Thus, the backing layer may have a flange or lip extending around theproximal face of the backing layer, of a transparent or translucentmaterial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

This bears a film of a light switchable adhesive to secure the dressingin place to prevent leakage on its proximal face, and a layer of opaquematerial on its distal face.

To remove the dressing and not cause excessive trauma in removal of thedressing, the layer of opaque material on the distal face of the flangeor lip extending around the wound is removed prior to application ofradiation of an appropriate wavelength to the flange or lip.

If the periphery of the wound dressing, outside the relativelyfluid-tight seal, that bears an adhesive film to attach it to the skinaround the wound, is of a material that has a high moisture vapourpermeability or is a switchable material, then the adhesive film, ifcontinuous, should also have a high or switchable moisture vapourpermeability, e.g. be an adhesive such as used in Smith & Nephew'sAllevyn™, IV3000™ and OpSite™ dressings.

In a number of main embodiments of the present invention (summarisedabove), irrigant and/or wound exudate is moved in and out of thedressing.

This may be done under negative pressure on the dressing. Such a vacuummay be used to hold the wound dressing in place in a fluid-tight sealaround the periphery of the wound-facing face of the wound dressing.

This removes the need for adhesives and associated trauma to thepatient's skin, and the wound dressing may be merely provided with asilicone flange or lip to seal the dressing around the wound.

Alternatively, the flow of irrigant and/or wound exudate in and out ofthe dressing may be under positive pressure, which will tend to act atperipheral points to lift and remove the dressing off the skin aroundthe wound.

In such use of the apparatus, it may thus be necessary to provide meansfor forming and maintaining such a seal or closure over the woundagainst such positive pressure on the wound, to act at peripheral pointsfor this purpose.

Examples of such means include light switchable adhesives, as above, tosecure the dressing in place to prevent leakage.

Since the adhesion of a light switchable adhesive is reduced byphotocuring, thereby reducing the trauma of removal of the dressing, afilm of a more aggressive adhesive may be used, e.g. on a flange, asabove.

Examples of suitable fluid adhesives for use in more extreme conditionswhere trauma to the patient's skin is tolerable include ones thatconsist essentially of cyanoacrylate and like tissue adhesives, appliedaround the edges of the wound and/or the proximal face of the backinglayer of the wound dressing, e.g. on a flange or lip.

Further suitable examples of such means include adhesive (e.g. withpressure-sensitive adhesive) and non-adhesive, and elastic andnon-elastic straps, bands, loops, strips, ties, bandages, e.g.compression bandages, sheets, covers, sleeves, jackets, sheathes, wraps,stockings and hose.

The latter include, e.g. elastic tubular hose or elastic tubularstockings that are a compressive fit over a limb wound to apply suitablepressure to it when the therapy is applied in this way.

Suitable examples also include inflatable cuffs, sleeves, jackets,trousers, sheathes, wraps, stockings and hose that are a compressive fitover a limb wound to apply suitable pressure to it when the therapy isapplied in this way. Such means may each be laid out over the wounddressing to extend beyond the periphery of the backing layer of thewound dressing.

As appropriate they may be adhered or otherwise secured to the skinaround the wound and/or itself and as appropriate will apply compression(e.g. with elastic bandages, stockings) to a degree that is sufficientto hold the wound dressing in place in a fluid-tight seal around theperiphery of the wound,

Such means may each be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached or releasably attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or these components may be a Velcro™, push snap ortwist-lock fit with each other.

The means and the dressing may be separate structures, permanentlyunattached to each other.

In a more suitable layout for higher positive pressures on the wound, astiff flange or lip extends around the periphery of the proximal face ofthe backing layer of the wound dressing as hereinbefore defined.

The flange or lip is concave on its proximal face to define a peripheralchannel or conduit.

It has a suction outlet that passes through the flange or lip tocommunicate with the channel or conduit and may be connected to a devicefor applying a vacuum, such as a pump or a piped supply of vacuum.

The backing layer may be integral with or attached, for example byheat-sealing, to the flange or lip extending around its proximal face.

To form the relatively fluid-tight seal or closure over a wound that isneeded and to prevent passage of irrigant and/or exudate under theperiphery of the wound-facing face of the wound dressing, in use of theapparatus, the dressing is set on the skin around the wound.

The device then applies a vacuum to the interior of the flange or lip,thus forming and maintaining a seal or closure acting at peripheralpoints around the wound against the positive pressure on the wound.

With all the foregoing means of attachment, and means for forming andmaintaining a seal or closure over the wound, against positive ornegative pressure on the wound at peripheral points around the wound,the wound dressing sealing periphery is preferably of a generally roundshape, such as an ellipse, and in particular circular.

As noted above, the cleansing means for selectively removing materialsthat are deleterious to wound healing from wound exudate, which means isunder the backing layer and sits in the underlying wound in use, oftencomprises a chamber. A permeable integer, e.g. a sheet, film ormembrane, forms part of the chamber wall.

In single-phase systems, the device to move fluid moves wound exudate inand out of the cleansing means through the permeable integer, either asa ‘circulating system’ or a reversing system.

In two-phase systems, the chamber contains a cleansing fluid, mostusually a fluid (dialysate) phase. The latter is separated from thewound exudate by means of the permeable integer. The fluid that is movedwithin the means for fluid cleansing by at least one device for movingfluid is the cleansing fluid. and/or the wound exudate optionally mixedwith irrigant.

The general features of the cleansing means of the present inventionwill now be described, followed by specific features related to specificcleansing means within the dressing.

The cleansing chamber is a resiliently flexible, e.g. elastomeric, andpreferably soft, structure with good conformability to wound shape.

It is favourably urged by its own resilience against the backing layerto apply gentle pressure on the wound bed.

The cleansing chamber may be integral with the other components of thedressing, in particular the backing layer.

Alternatively, it may be permanently attached to them/it, with anadhesive film, for example, or by heat-sealing, e.g. to a flange or lipextending from the proximal face, so as not to disrupt the relativelyfluid-tight seal or closure over the wound that is needed.

Less usually, the cleansing chamber is releasably attached to thebacking layer, with an adhesive film, for example, or these componentsmay be a push, snap or twist-lock fit with each other.

The cleansing chamber and the backing layer may be separate structures,permanently unattached to each other.

It may be in the form of, or comprise one or more conformable hollowbodies defined by a film, sheet or membrane, such as a bag, cartridge,pouch or other like structure.

The film, sheet or membrane, often has a (generally uniform) thicknessof up to 1 mm, preferably up to 500 micron, more preferably from 20micron to 500 micron minimum thickness, and is often resilientlyflexible, e.g. elastomeric, and preferably soft.

Such a film, sheet or membrane is often integral with the othercomponents of the dressing, in particular the backing layer, orpermanently attached to them/it, with an adhesive film, for example, orby heat-sealing, e.g. to a flange.

However, when used herein the term ‘chamber’ includes any hollow body orbodies defined by a film, sheet or membrane, and is not limited to abag, pouch or other like structure.

It may be formed of a film, sheet or membrane of a polymeric material isin a more convoluted form.

This may be in the form of elongate structures, such as pipes, tubeshollow fibres or filaments or tubules, e.g. in an array with spacestherebetween, running between an inlet and an outlet manifold.

The chamber, especially when it is a bag, cartridge, pouch or other likestructure in which the cleansing fluid is contained, may suitably fillmuch or all of the wound space when in use during wound therapy. It maybe desired to limit the remaining wound space volume under the backinglayer with a filler where this is not the case, or to adjust the volumeof the chamber to do so.

Where the chamber and the backing layer are separate structures, notdirectly attached to each other, such a filler may conveniently liebetween the chamber and the backing layer to separate the structures, orwithin the chamber, so that the chamber may lie directly in contact withthe wound bed.

The filler is favourably a resiliently flexible, e.g. elastomeric, andpreferably soft, structure with good conformability to wound shape. Thechamber may be urged by its own resilience and that of the filler toapply gentle pressure on the wound bed.

Examples of suitable forms of such wound fillers include foams formed ofa suitable material, e.g. a resilient thermoplastic. Preferred materialsfor the present wound dressing include reticulated filtrationpolyurethane foams with small apertures or pores. (Examples of such afiller are shown in FIGS. 7, 10, 11 and 13 hereinafter.)

Alternatively or additionally, it may be in the form of, or comprise oneor more conformable hollow bodies defined by a film, sheet or membrane,such as a bag, pouch or other structure, filled with a fluid or solidthat urges it to the wound shape.

Examples of suitable fluids contained in the hollow body or bodiesdefined by a film, sheet or membrane include gases, such as air,nitrogen and argon, more usually air, at a small positive pressure aboveatmospheric; and liquids, such as water, saline.

Examples also include gels, such as silicone gels, e.g. CaviCare™ gel,or preferably cellulosic gels, for example hydrophilic cross-linkedcellulosic gels, such as Intrasite™ cross-linked materials. Examplesalso include aerosol foams, where the gaseous phase of the aerosolsystem is air or an inert gas, such as nitrogen or argon, more usuallyair, at a small positive pressure above atmospheric; and solidparticulates, such as plastics crumbs.

Such a filler may be inflatable and deflatable with the fluid, such as agas, e.g. air or nitrogen, or a liquid, such as water or saline, toapply varying pressure to the chamber and wound space if provided withone or more inlet and/or outlet pipes.

Of course, if the backing layer is a sufficiently conformable and/ore.g. a downwardly dished sheet, the backing layer may lie under thewound filler, rather than vice versa. FIG. 6 shows such a resilientlyflexible, balloon filler, which is inflatable and deflatable with afluid, defined by the backing layer and a rigid polymer dome that isimpermeable and permanently attached to the distal face of the backinglayer

In this type of layout, in order for the wound filler to urge the wounddressing towards the wound bed, it will usually have to be firmlyadhered or otherwise releasably attached to the skin around the wound.This is especially the case in those embodiments where the wound fillerand the backing layer are separate structures, permanently unattached toeach other. FIG. 7 shows a variant of the apparatus with such aresiliently flexible balloon filler above the backing layer.

The specific nature of the chamber will depend largely on the type ofcleansing means that is employed.

The apparatus of the invention for aspirating, irrigating and/orcleansing wounds is provided with means for fluid cleansing, which maybe

-   a) a single-phase system, such as an ultrafiltration unit, or a    chemical adsorption unit; or-   b) a two-phase system, such as a dialysis unit.

In the former, fluid from the wound passes through a single flow path inwhich materials deleterious to wound healing are removed and thecleansed fluid, still containing materials that are beneficial inpromoting wound healing is returned to the wound.

Examples of such systems are shown in FIGS. 1 and 2 hereinafter.

The means for fluid cleansing in such a system may include a macro- ormicrofiltration unit, which appropriately comprises one or moremacroscopic and/or microscopic filters. These are to retainparticulates, e.g. cell debris and micro-organisms, allowing proteinsand nutrients to pass through.

The membrane may preferably be of a hydrophilic polymeric material, suchas a cellulose acetate-nitrate mixture, polyvinylidene chloride, and,for example hydrophilic polyurethane.

Examples of less preferred materials include hydrophobic materials alsoincluding polyesters, such as polycarbonates, PTFE, and polyamides, e.g.6-6 and 6-10, and hydrophobic polyurethanes, and quartz and glass fibre.

It has microapertures or micropores, the maximum cross-dimension ofwhich will largely depend on the species that are to be selectivelyremoved in this way and those to which it is to be permeable.

The former may be removed with microapertures or micropores, e.g.typically with a maximum cross-dimension in the range of 20 to 700micron, e.g. 20 to 50 nm (for example for undesired proteins), 50 to 100nm, 100 to 250 nm, 250 to 500 nm and 500 to 700 nm.

Alternatively, this part of a means for wound exudate cleansing may beessentially a stack of such filters connected in series with decreasingcross-dimension of the apertures or pores in the direction of the fluidflow.

It may include an ultrafiltration unit, which appropriately comprisesone or more ultrafiltration filters, such as one in which the cleansinginteger is a filter for materials deleterious to wound healing, forexample a high throughput, low protein-binding polymer film, sheet ormembrane which is selectively impermeable to materials deleterious towound healing, which are removed and the cleansed fluid, stillcontaining materials that are beneficial in promoting wound healing ispassed by it.

The permeable integer in such a system may be a selective low pass'system film, sheet or membrane with relatively small apertures or pores.

Suitable materials for the filter include those organic polymers listedabove for macro- and micro-filters.

It will be appropriate to design and run the apparatus with this type ofcleansing means as a ‘circulating system’, in which the relevant fluidpasses through the cleansing means one or more times in only onedirection, since this is necessary for retaining the filter residue outof the wound exudate.

(it would be inappropriate to run the system in the form of a ‘reversingsystem’, since the fluid passing through the cleansing means at leastonce in the reverse direction would return these materials into thewound.)

The filter integer may be a flat sheet or membrane of a polymericmaterial, or (less usually) in a more convoluted form, e.g. in the formof elongate structure, such as pipes, tubules, etc.

It may be intended that respectively the chamber or the dressing isdisposable. In such case, the device for moving fluid through the meansfor wound exudate cleansing is then started and run until no significantamounts of materials deleterious to wound healing remain in the wound.

The dressing and/or the cleansing chamber under the backing layer isthen removed and discarded, to remove the materials deleterious to woundhealing from wound exudate.

A single-phase system cleansing means may comprise a chemical adsorptionunit, for example one in which a particulate, such as a zeolite, or alayer, e.g. of a functionalised polymer has sites on its surface thatare capable of removing materials deleterious to wound healing onpassing the fluid from the wound over them.

The materials may be removed, e.g. by destroying or binding thematerials that are deleterious to wound healing, by, for examplechelators and/or ion exchangers, and degraders, which may be enzymes.

In this type, the chamber wall film, sheet or membrane is not an integerselectively permeable to materials deleterious to wound healing. Thechamber, however, contains one or more materials that can removematerials deleterious to wound healing from wound exudate, by beingantagonists to such species.

For example, where the wound exudate contains

proteases, such as serine proteases, e.g. elastase, and thrombin;cysteine proteases, matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases;endotoxins, such as lipopolysaccharides;inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment);pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β),oxidants, such as free radicals, e.g., e.g. peroxide and superoxide; andmetal ions, e.g. iron II and iron 111; all involved in oxidative stresson the wound bed, orbasic or acidic species which adversely affect the pH in the woundexudate, such as protons,the cleansing chamber may contain, behind the permeable integer at leastone of the following antagonists as appropriate that is captive in apart of the chamber where it can be in contact with the irrigant and/orwound exudate: protease inhibitors, such as serine protease inhibitors,such as 4-(2-aminoethyl)-benzene sulphonyl fluoride (AEBSF, PefaBloc)and Nα-p-tosyl-L-lysine chloromethyl ketone (TLCK) andε-aminocaproyl-p-chlorobenzylamide; cysteine protease inhibitors; matrixmetalloprotease inhibitors; and carboxyl (acid) protease inhibitors;binders and/or degraders, such as anti-inflammatory materials to bind ordestroy lipopolysaccharides, e.g. peptidomimetics;anti-oxidants, such as 3-hydroxytyramine (dopamine), ascorbic acid(vitamin C), vitamin E and glutathione, and stable derivatives thereof,and mixtures thereof; to relieve oxidative stress on the wound bed:metal ion chelators and/or ion exchangers, such as transition metal ionchelators, such as iron III chelators (Fe III is involved in oxidativestress on the wound bed.), such as desferrioxamine (DFO),3-hydroxytyramine (dopamine); iron III reductants; oragents for the adjustment of pH in the wound exudate, such as base oracid scavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich).

It will be appropriate to design and run the apparatus with this type ofcleansing means either as a ‘circulating system’, or in the form of a‘reversing system’, since the fluid passing through the cleansing meansat least once in the reverse direction would not return these materialsinto the wound.)

An example of such systems is shown inter alia in FIGS. 1, 6 and 7(reversing system) and 2, 8 and 9 (circulating system) hereinafter.

A second, selectively permeable integer, again suitably a flat sheet ormembrane of a polymeric material may be required to form part of adistal chamber wall in the flowpath in any appropriate part of theapparatus to retain materials that are deleterious to wound healing andantagonists or other active materials in the chamber.

A particular advantage of this form of the system, is that where amaterial that can remove materials deleterious to wound healing fromwound exudate is (cyto)toxic or bioincompatible, or not inert to anycomponents that are beneficial in promoting wound healing, the systemdoes not allow any significant amounts of it to pass into the wound.

In two-phase systems, the chamber contains a cleansing fluid, mostusually a fluid (dialysate) phase. The latter is separated from thewound exudate by means of a permeable integer.

At least one fluid is moved through the means for fluid cleansing by atleast one device, in particular across the permeable integer, forexample the polymer film, sheet or membrane.

This promotes the passage of relatively high concentrations of solutesor disperse phase species, including deleterious materials, from thewound exudate into the cleansing fluid and the chamber and optionallythe system in which the cleansing fluid recirculates. Such systems aredescribed further below.

The fluid that is moved through the means for fluid cleansing by thedevice for moving fluid is

a) the cleansing fluid orb) the wound exudate optionally mixed with irrigant, orc) both.

Examples of such systems are shown in FIGS. 12 and 13 hereinafter, inwhich

FIGS. 12 a and 13 show such a system, a dialysis unit, in which only thecleansing fluid separated from the wound exudate is the moving fluid.

FIG. 12 b shows such a system, a dialysis unit, in which the cleansingfluid and the wound exudate optionally with irrigant are the movingfluids.

The cleansing fluid is less usually static as in FIG. 4, as this may notbe a system with sufficient (dynamic) surface area to remove materialsdeleterious to wound healing from wound exudate at a practical rate.

Typical dialysate flow rates in a dialytic means for fluid cleansing inthe present apparatus for aspirating, irrigating and/or cleansing woundsare those used in the conventional type of two-phase system, such as adialysis unit for systemic therapy.

The integer may be a film, sheet or membrane, often of the same type,and of the same (generally uniform) thickness, as those used inconventional two-phase system, such as a dialysis unit for systemictherapy.

As noted above, the film, sheet or membrane may be substantially flat,but, especially where the cleansing fluid circulates, it may moresuitably be in the form of pipes, tubes or tubules in an array.

The surface area of any such film, sheet or membrane may be suitably beno less than 50 mm², such 100 to 1000000 mm², e.g. 500 to 25000 mm².

If both fluids move it may be in co- or preferably counter-currentdirection.

Again, materials deleterious to wound healing are removed into thedialysate, and the cleansed fluid, still containing materials that arebeneficial in promoting wound healing, remains or is returned byrecirculation to the wound.

Examples of these deleterious materials as above include

oxidants, such as free radicals, e.g. peroxide and superoxide;iron II and iron III; all involved in oxidative stress on the wound bed;proteases, such as serine proteases, e.g. elastase and thrombin;cysteine proteases, matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases;endotoxins, such as lipopolysaccharides;autoinducer signalling molecules, such as homoserine lactonederivatives, e.g. oxo-alkyl derivatives;inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment)pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β); andinflammatories, such as lipopolysaccharides, and e.g. histamine; andbasic or acidic species which adversely affect the pH in the woundexudate, such as protons.

Examples of suitable materials for the film, sheet or membrane(typically in the form of conformable hollow bodies defined by the film,sheet or membrane, such as the structures described hereinbefore)include natural and synthetic polymeric materials.

The membrane may be of one or more hydrophilic polymeric materials, suchas a cellulose derivative, e.g. regenerated cellulose, a cellulosemono-, di- or tri-esters, such as cellulose mono-, di- or tri-acetate,benzyl cellulose and Hemophan, and mixtures thereof.

Examples of other materials include hydrophobic materials, such asaromatic polysulphones, polyethersulphones, polyetherether-sulphones,polyketones, polyetherketones and polyetherether-ketones, andsulphonated derivatives thereof, and mixtures thereof.

Examples of other materials include hydrophobic materials, such aspolyesters, such as polycarbonates and polyamides, e.g. 6-6 and 6-10;polyacrylates, including, e.g. poly(methyl methacrylate),polyacrylonitrile and copolymers thereof, for exampleacrylonitrile-sodium metallosulphonate copolymers; and poly(vinylidenechloride).

Suitable materials for the present membranes include thermoplasticpolyolefins, such as polyethylene e.g. high-density polyethylene,polypropylene, copolymers thereof, for example with vinyl acetate andpolyvinyl alcohol, and mixtures thereof.

The dialysis membrane should have a molecular weight cut off (MWCO)chosen to allow selective perfusion of species deleterious to woundhealing that have been targeted for removal from the wound. For example,perfusion of the serine protease elastase (molecular weight 25900Dalton) would require a membrane with MWCO>25900 Dalton. The MWCOthreshold can be varied to suit each application between 1 and 3000000Dalton.

Preferably, the MWCO should be as close as possible to this weight toexclude interference by larger competitor species.

For example, such a membrane with MWCO >25900 Dalton does not allow anysignificant amounts of the antagonist to elastase, alpha-1-antitrypsin(AAT) (molecular weight 54000 Dalton), which occurs naturally in wounds,to diffuse freely out of the wound fluid into the dialysate. Theinhibitor, which is beneficial in promoting chronic wound healing,remains in contact with the wound bed, and can act beneficially on it,whilst the elastase that is deleterious to wound healing is removed.

Such use of the present apparatus is, e.g. favourable to the woundhealing process in chronic wounds, such as diabetic foot ulcers, andespecially decubitus pressure ulcers.

As noted hereinafter, antagonists, for example degrading enzymes, orsequestrating agents for elastase on the dialysate side of the membrane,may be used to enhance the removal of this protease from wound exudate.

A less conventional type of two-phase system (see above) may be used asthe means for fluid cleansing. In this type, the dialysis polymer film,sheet or membrane is not an integer selectively permeable to materialsdeleterious to wound healing, such as

proteases, such as serine proteases, e.g. elastase, and thrombin;cysteine proteases; matrix metalloproteases, e.g. collagenase; andcarboxyl (acid) proteases;endotoxins, such as lipopolysaccharides;inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), plasminogenactivator inhibitor, or angiostatin (plasminogen fragment)pro-inflammatory cytokines such as tumour necrosis factor alpha (TNFα)and interleukin 1 beta (IL-1β);oxidants, such as free radicals, e.g., e.g. peroxide and superoxide; andmetal ions, e.g. iron II and iron III; all involved in oxidative stresson the wound bed; andbasic or acidic species which adversely affect the pH in the woundexudate, such as protons.

It will however also permit components of the exudate from a woundand/or irrigant fluid that may be larger or smaller molecules, but arebeneficially involved in wound healing to pass into and through it.

In the dialysate, or preferably in one or more solid structural integerswith at least one surface in contact with the dialysate, in the meansfor fluid cleansing, there are one or more materials that can removematerials deleterious to wound healing from wound exudate, by being

antagonists to such species, for example enzymes or others, such asprotease inhibitors, such as serine protease inhibitors, such as4-(2-aminoethyl)-benzene sulphonyl fluoride (AEBSF, PefaBloc) andNα-p-tosyl-L-lysine chloromethyl ketone (TLCK) andε-aminocaproyl-p-chlorobenzylamide; cysteine protease inhibitors; matrixmetalloprotease inhibitors; and carboxyl (acid) protease inhibitors;binders and/or degraders, such as anti-inflammatory materials to bind ordestroy lipopolysaccharides, e.g. peptidomimetics;anti-oxidants, such as 3-hydroxytyramine (dopamine), ascorbic acid(vitamin C), vitamin E and glutathione, and stable derivatives thereof,and mixtures thereof; to relieve oxidative stress on the wound bed;metal ion chelators and/or ion exchangers, such as transition metal ionchelators, such as iron III chelators (Fe III is involved in oxidativestress on the wound bed.), such as desferrioxamine (DFO),3-hydroxytyramine (dopamine); iron III reductants; andagents for the adjustment of pH in the wound exudate, such as base oracid scavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich).

They further include peptides (including cytokines, e.g. bacterialcytokines, such as α-amino-γ-butyrolactone and L-homocarnosine); and

sacrificial redox materials that are potentially or actually beneficialin promoting wound healing, such as iron III reductants; and/orregeneratable materials of this type, such as glutathione redox systems;andother physiologically active components.

In use of the two-phase system dialysis unit, of this less conventionaltype, a broad spectrum of species will usually pass into the dialysatefrom the exudate.

Some (mainly ionic) species will pass from the dialysate into theirrigant and/or wound exudate through the dialysis polymer film, sheetor membrane that is not very selectively permeable to materialsdeleterious to wound healing.

The components of the exudate from a wound and/or irrigant fluid willdiffuse freely to and fro through it.

A steady state concentration equilibrium is eventually set up betweenthe dialysate and the irrigant and/or wound exudate, which is ‘toppedup’ from the wound dressing.

Circulating wound fluid aids in the quicker attainment of thisequilibrium of materials beneficial in promoting wound healing.

It also returns them to the site where they can be potentially of mostbenefit, i.e. the wound bed.

The target materials deleterious to wound healing also pass into thedialysate from the exudate through the dialysis polymer film, sheet ormembrane that is not very selectively permeable to materials deleteriousto wound healing.

Unlike the other components of the exudate from a wound and/or irrigantfluid, the target materials deleterious to wound healing come intocontact with the dialysate, or preferably with one or more solidstructural integers with at least one surface in the dialysate, and areremoved by the appropriate antagonists, binders and/or degraders,chelators and/or ion exchangers and redox agents, etc. The cleansedfluid, still containing some materials that are beneficial in promotingwound healing, is returned to the wound.

Unlike the other components of the exudate from a wound and/or irrigantfluid the target materials are constantly removed from the dialysate,very little of these species will pass from the dialysate into theirrigant and/or wound exudate, and a steady state concentrationequilibrium is not set up, even if the species are constantly ‘toppedup’ from the wound dressing.

It is believed that circulating one or both fluids aids in removal fromrecirculation of the materials deleterious to wound healing from woundexudate, whilst retaining materials that are beneficial in promotingwound healing in contact with the wound.

A particular advantage of this form of the two-phase system, is thatwhere a material that can remove materials deleterious to wound healingfrom wound exudate is (cyto)toxic or bioincompatible, or not inert toany components that are beneficial in promoting wound healing, thesystem does not allow any significant amounts of antagonist to diffusefreely out of the dialysate into the wound fluid. The active materialcan act beneficially on the fluid however.

The film sheet or membrane is preferably a dialysis membrane ofmolecular weight cut off (MWCO) (as conventionally defined) chosen toallow perfusion of species targeted for sequestration or destruction.

For example, sequestration of the serine protease elastase (molecularweight 25900 Dalton) would require a membrane with MWCO >25900 Dalton.

The MWCO threshold can be varied to suit each application between 1 and3 000 000 Dalton. Preferably, the MWCO should be as close as possible tothis weight to exclude sequestering interference by larger competitorspecies.

It will be seen that in many of the embodiments of the apparatus of thisfirst aspect of the present invention for cleansing wounds, the irrigantand/or wound exudate and/or the cleansing fluid passes from the wounddressing and is returned via a return path to it, through or under thebacking layer with a wound-facing face which is capable of forming arelatively fluid-tight seal or closure over a wound.

Each return path will require

at least one inlet pipe for connection to a fluid return tube, whichpasses through the wound-facing face of the backing layer, andat least one outlet pipe for connection to a fluid offtake tube, whichpasses through the wound-facing face of the backing layer,the point at which the or each inlet pipe and the or each outlet pipepasses through or under the wound-facing face forming a relativelyfluid-tight seal or closure over the wound.

Where any pipe is described in connection with the operation of theapparatus as being connected or for connection to a (mating end of a)tube, the pipe and the tube may form a single integer.

Where the mode of running the present apparatus is in the form of a‘reversing system’, the at least one inlet pipe and the at least oneoutlet pipe, and the at least one fluid supply tube and the at least oneoutlet pipe, may respectively be the same integer.

This is often in a ‘multiple-pass system’ for irrigant and/or woundexudate where this fluid passes from the wound dressing and is returnedto the wound, in both cases via the cleansing means, e.g. under theaction of the movement of a reciprocating pump, such as a syringe orpiston pump.

The or each inlet pipe or outlet pipe may have the form of an aperture,such as a funnel, hole, opening, orifice, luer, slot or port forconnection as a female member respectively to a mating end of a fluidreturn tube or a fluid offtake tube (optionally or as necessary viameans for forming a tube, pipe or hose, or nozzle, as a male member.

Where the components are integral they will usually be made of the samematerial (for which it will be understood that materials that are listedabove are amongst those that are suitable).

Where, alternatively, they are a push, snap or twist-lock fit, the maybe of the same material or of different materials. In either case,materials that are listed above are amongst those that are suitable forall the components.

The backing layer may often have a rigid and/or resiliently inflexibleor stiff area to resist any substantial play between the or each pipeand the or each mating tube, or deformation under pressure in anydirection.

It may often be stiffened, reinforced or otherwise strengthened by aboss projecting distally (outwardly from the wound).

This is usually around each relevant tube, pipe or hose, or nozzle,hole, opening, orifice, luer, slot or port for connection to a matingend of a fluid return tube or fluid offtake tube.

Alternatively or additionally, where appropriate the backing layer mayhave a stiff flange or lip extending around the proximal face of thebacking layer to stiffen, reinforce or otherwise strengthen the backinglayer.

Both the single-phase system, such as an ultrafiltration unit, andtwo-phase system, such as a dialysis unit, may be in modular form thatis relatively easily demountable from the apparatus of the invention.

Each return flow path (whether in a single-phase system or a two-phasesystem, such as an dialysis unit) requires a means for moving fluid.

Suitable means will be apparent to the skilled person, but the followingtypes of small pump may be used as desired:

small reciprocating pumps, such as:

-   diaphragm pumps—where pulsations of one or two flexible diaphragms    displace liquid while check valves control the direction of the    fluid flow.    syringe and piston-   pumps—where pistons pump fluids optionally through check valves, in    particular for variable and/or reversible positive and/or negative    pressure on the wound bed and for closed single-phase reversing    system, in which the wound exudate and/or irrigant passes to and fro    through the cleansing means.    small rotary pumps, such as:-   rotary vane pumps—with rotating vaned disk attached to a drive shaft    moving fluid without pulsation as it spins. The outlet can be    restricted without damaging the pump.-   peristaltic pumps—with peripheral rollers on rotor arms acting on a    flexible fluid circulation tube to urge fluid current flow in the    tube in the direction of the rotor, in particular for a dialysate    phase in a multiple-phase circulating system, in which it passes in    only one direction.

The type and/or capacity of the device will be largely determined by theappropriate or desired fluid volume flow rate of irrigant and/or woundexudate from the wound for optimum performance of the wound healingprocess, and by factors such as portability, power consumption andisolation from contamination.

Such a device may also suitably be one that is capable of pulsed,continuous, variable, reversible and/or automated and/or programmablefluid movement. It may in particular be a pump of any of these types.

The main function of the invention, i.e. an apparatus, that isadvantageously portable, for irrigating and/or cleansing wounds willlargely determine the main function of the pump, i.e. a moving devicefor moving fluid, e.g. (chronic) wound exudate, through the cleansingmeans, rather than for aspirating or pressurising wounds that are beingcleansed.

It may however be used to apply a positive or negative pressure of up to50% atm., more usually up to 15% atm., to the wound, which may bepulsed, continuous, variable, reversible, automated and/or programmable,as for fluid movement.

A fluid-tight seal or closure of the wound dressing around the peripheryof the backing layer then becomes more crucial, if wound cleansing is tobe applied in this way.

The device is favourably a small peristaltic pump or diaphragm pump,e.g. preferably a miniature portable diaphragm or peristaltic pump.These are preferred types of pump, in order in particular to reduce oreliminate contact of internal surfaces and moving parts of the pump with(chronic) wound exudate, and for ease of cleaning.

Where the pump is a diaphragm pump, and preferably a small portablediaphragm pump, the one or two flexible diaphragms that displace liquidmay each be, for example a polymer film, sheet or membrane, that isconnected to means for creating the pulsations. This may be provided inany form that is convenient, inter alia as an electromechanicaloscillator, a piezoelectric transducer, a core of a solenoid or aferromagnetic integer and coil in which the direction of current flowalternates, a rotary cam and follower, and so on

In one embodiment of the apparatus of this first aspect of the presentinvention for cleansing wounds with a two-phase system, such as one witha dialysis unit, no fluid passes from the wound dressing or is returnedvia a return path to it, through the backing layer.

It therefore does not require any inlet pipe for connection to a fluidreturn tube or any outlet pipe for connection to a fluid offtake tube,which passes through the wound-facing face of the backing layer.

In such an embodiment, the prime purpose of the moving device is to movethe cleansing fluid. In such an embodiment, amongst suitable devicesare:

Suitable examples of such a dressing include, e.g. those making use ofrotary impellers, such as: vane impellers, with rotating vaned diskattached to a drive shaft, propellers on a drive shaft, etc.

Such devices may be integral with the dressing. It will be seen that thecorresponding apparatus disadvantageously has a need to ensure afluid-tight seal or closure of the chamber around any part of the movingdevice where it passes through the chamber wall or wound dressing. Theymay (disadvantageously) not be portable.

The possibility of using this type of wound dressing may be largelydetermined by the ability to achieve such a relatively fluid-tight sealor closure. It may be desirable that no part of the moving device passthrough the chamber wall or wound dressing.

They may be separate structures, capable of interacting as appropriatefor the purpose of moving cleansing fluid along a desired flow pathacross the selectively permeable integer, effectively in a‘multiple-pass system’ within the interior of the chamber.

The moving device may drive the cleansing fluid inside the chamberremotely to set it in motion.

Such an embodiment of the apparatus advantageously enables a tight sealor closure over the wound, and no part of the moving device need passthrough the chamber wall or wound dressing.

This avoids the need to ensure a fluid-tight seal or closure of thechamber around it.

The chamber may thus, e.g. be provided in a form with at least onemagnetic follower enclosed within it and acted upon by a magneticstirrer to impel the cleansing fluid. The magnetic stirrer to impel thecleansing fluid may be mounted on, e.g. releasably attached to the othercomponents of the dressing, in particular the backing layer, e.g. with aVelcro™ attachment, an adhesive film (e.g. of pressure-sensitiveadhesive) or elastic or non-elastic straps, bands, ties, bandages, e.g.compression bandages, sheets or covers, or be a push, snap or twist-lockfit with it/tem.

It may be mounted, e.g. centrally, on the backing layer above a circularor concentric toroidal hollow body that effectively forms an annularchamber provided with at least one magnetic follower within it. In use,the magnetic stirrer impels the magnetic follower enclosed withinrespectively the circular or the annular chamber to cause the woundcleansing fluid to circulate.

The film, sheet or membrane is often selectively permeable, contains thecleansing fluid, and should have the right resilience against thepulsing pressure to allow significant compression or decompression ofthe chamber to recirculate the wound cleansing fluid through it.

All such remote devices may be integral with or permanently attached tothe dressing, in particular the backing layer, with an adhesive film,for example, or by heat-sealing.

These components may be releasably attached, e.g. by a Velcro™attachment, with an adhesive film (e.g. with pressure-sensitiveadhesive) or with elastic and non-elastic straps, bands, ties, bandages,e.g. compression bandages, sheets or covers.

Another such a device may be provided in the form of at least one ballor sphere, e.g. a solid metal ball or sphere.

This sets the cleansing fluid is in motion in contact with the surfaceof the integer that is selectively permeable to materials in the woundexudate under the action of the bodily movement of the patient.

Alternatively, the top of a compressible chamber may be provided with atrackway, around which the patient may run his or her fingers to movethe fluid around the chamber.

In practice, even from a wound in a highly exuding state, such a rate ofexudate flow is only of the order of up to 75 microlitres/cm²/hr (wherecm² refers to the wound area), and the fluid can be highly mobile (owingto the proteases present).

Exudate levels drop and the consistency of wound exudate changes, e.g.to a higher viscosity liquid, as the wound heals, e.g. to a level forthe same wound that equates to 12.5-25 microlitres/cm²/hr.

Where materials deleterious to wound healing are removed by a two-phasesystem (See below.), such as a dialysis unit, fluid is also potentiallylost to the system through the means for fluid cleansing.

This may occur, e.g. through a dialysis polymer film, sheet or membranewhich is also permeable to water, in addition to materials deleteriousto wound healing.

The balance of fluid in recirculation may thus further decrease. It maybe desired to adjust the volume of the irrigant and/or wound exudate andhence to minimise this undesired loss.

If the consistency of wound exudate changes, e.g. to a higher viscosityliquid, as the wound heals, it may be desired to adjust the volume ofthe irrigant and/or wound exudate and hence to adjust the viscosity ofthe liquid, e.g. to a level that equates to the initial level.

As noted above, the apparatus of this first aspect of the presentinvention for cleansing wounds may be used with the wound space atatmospheric pressure or at a positive or negative pressure of up to 50%atm., more usually up to 15% atm. applied to the wound.

A fluid may be added to or removed from the wound space before and/orduring wound therapy as may be desired to adjust the volume of theirrigant and/or wound exudate and/or to adjust the neutral, positive ornegative pressure on the wound.

Thus, the volume of irrigant and/or wound exudate from the wound may beincreased by continuing addition of irrigant to the wound space. Apositive pressure may be applied to the wound by for example flooding itwith a desired amount of irrigant before the dressing is applied to itand/or by continuing addition of irrigant to the wound during the run. Anegative pressure may be applied to the wound by means of fluid removalfrom the wound, for example with a small pump.

This may be achieved in all cases by passage of the relevant fluidfreely to and fro through a fluid regulator, such as a valve or othercontrol device, e.g. a valve that is turned to switch between open andclosed, that is mounted in a pipe or tube that passes through or underthe backing layer.

For example, if exudate build-up under the backing layer becomesexcessive during use, a bleed valve may be opened and excess fluidvented off, e.g. to a waste reservoir, and any excess pressure relieved.

Equally, any loss from any fluid from the wound may be adjusted, or apositive pressure (i.e. above-atmospheric pressure) may be applied tothe wound bed by means of an irrigant which passes through a similarinput regulator, such as a valve or other control device, e.g. a valvethat is turned to switch between on and off, through or under thebacking layer to the wound bed.

A negative pressure may be conveniently applied to the wound bed bymeans of fluid removal from the wound, for example with a small pump,through a similar vacuum regulator, such as a valve or other controldevice, e.g. a valve that is turned to closure once the vacuum has beenapplied, before disconnection of the vacuum source.

Alternatively or additionally, where appropriate the backing layer mayhave a regulator such as an injection septum, through which the desiredamount of the relevant fluid, such as irrigant, may be removed from orsupplied to the wound, for example with a small syringe or like pump toachieve the desired effect.

Equally, the balance in any cleansing fluid may be adjusted by means forbleeding or supplying fluid to the relevant flowpath. The means forbleeding or supplying fluid to the relevant flowpath may be situated inany appropriate part of the apparatus that is in contact with thecleansing fluid.

The means for bleeding or supplying fluid to the flowpath may be aregulator, such as a valve or other control device, e.g. a valve that isturned to switch between bleed and closure, for bleeding fluids from theapparatus, e.g. to a waste reservoir, such as a collection bag, or toswitch between supply and closure, for supplying fluids to theapparatus.

Alternatively or additionally, where appropriate the flowpath may have aregulator such as an injection septum, through which the desired amountof the relevant fluid cleanser may be removed from or supplied to theflowpath, e.g. with a small syringe or like pump to achieve the desiredeffect.

The inlet and/or outlet pipes, the fluid return tube and the fluidofftake tube, etc. where present may be of conventional type, e.g. ofelliptical or circular cross-section, and may suitably have a uniformcylindrical bore, channel, conduit or passage throughout their length.

Depending on the desired fluid volume flow rate of irrigant and/or woundexudate from the wound, and the desired amount in recirculation,suitably the largest cross-dimension of the bore may be up to 10 mm forlarge torso wounds, and up to 2 mm for limb wounds.

The tube walls should suitably thick enough to withstand any positive ornegative pressure on them.

This is in particular the case if the volume of irrigant and/or woundexudate from the wound in recirculation is increased by continuingaddition to it of wound exudate, and/or fluid passing from a cleansingfluid through a selectively permeable integer, for example the polymerfilm, sheet or membrane of a two-phase system, such as an dialysis unit.However, as noted above with regard to pumps, the prime purpose of suchtubes is to convey irrigant and exudate through the length of theapparatus flow path, rather than to act as pressure vessels. The tubewalls may suitably be at least 25 micron thick.

The whole length of the apparatus for aspirating, irrigating and/orcleansing wounds should be microbe-impermeable once the wound dressingis over the wound in use.

It is desirable that the wound dressing and the interior of theapparatus for aspirating, irrigating and/or cleansing wounds of thepresent invention is sterile.

The fluid may be sterilised in the system in which the fluid moves,including the means for fluid cleansing, by ultraviolet, gamma orelectron beam irradiation. This way, in particular reduces or eliminatescontact of internal surfaces and the fluid with any sterilising agent.

Examples of other methods of sterilisation of the fluid also includee.g. the use of

ultrafiltration through microapertures or micropores, e.g. of 0.22 to0.45 micron maximum cross-dimension, to be selectively impermeable tomicrobes; andfluid antiseptics, such as solutions of chemicals, such as chlorhexidineand povidone iodine; metal ion sources, such as silver salts, e.g.silver nitrate; and hydrogen peroxide;although the latter involve contact of internal surfaces and the fluidwith the sterilising agent.

It may be desirable that the interior of the wound dressing, the rest ofthe system in which the fluid recirculates, and/or the wound bed, evenfor a wound in a highly exuding state, are kept sterile, or that atleast naturally occurring microbial growth is inhibited.

It is also desirable to provide a system in which physiologically activecomponents of the exudate that are beneficial to wound healing are notremoved before or after the application of fluid cleansing, e.g. by thepassive deposition of materials that are beneficial in promoting woundhealing, such as proteins, e.g. growth factors.

This may occur at any point in the system that is in contact with suchphysiologically active components of the exudate that are beneficial towound healing.

Often this will occur at any point in the system that is in contact withthe exudate, usually in a single-phase system, but it may occur in thesecond fluid (dialysate) phase in a multiple-phase system wherematerials in the wound exudate that are potentially beneficial to woundhealing diffuse freely into that phase in use of the apparatus.

The deposition of materials that are beneficial in promoting woundhealing may be combated by using a repellent coating at any point or onany integer in direct contact with the relevant fluid.

Examples of coating materials for surfaces over which the circulatingfluid passes include

anticoagulants, such as heparin, andhigh surface tension materials, such as PTFE, and polyamides,which are useful for growth factors, enzymes and other proteins andderivatives.

In all embodiments of the apparatus the type and material of any tubesthroughout the apparatus of the invention for irrigating and/orcleansing wounds will be largely determined by their function.

To be suitable for use, in particular on chronic timescales, thematerial should be non-toxic and biocompatible, inert to any activecomponents, as appropriate of the irrigant and/or wound exudate and ofany dialysate. It should not allow any significant amounts ofextractables to diffuse freely out of it in use of the apparatus.

It should be sterilisable by ultraviolet, gamma or electron beamirradiation and/or with fluid antiseptics, such as solutions ofchemicals, fluid- and microbe-impermeable once in use, and flexible.

Examples of suitable materials include synthetic polymeric materials,such as polyolefins, such as polyethylene, e.g. high-densitypolyethylene and polypropylene.

Suitable materials for the present purpose also include copolymersthereof, for example with vinyl acetate and mixtures thereof. Suitablematerials for the present purpose further include medical gradepoly(vinyl chloride).

For the purposes of fluid cleansing in the apparatus of the presentinvention, both the single-phase system, such as an ultrafiltrationunit, and two-phase system, such as a dialysis unit, may have captive(non-labile, insoluble and/or immobilised) species such as thefollowing, bound to an insoluble and/or immobilised) substrate overand/or through which the irrigant and/or wound exudate from, the wounddressing passes in turn to the fluid return tube(s): antioxidants andfree radical scavengers, such as 3-hydroxytyramine (dopamine), ascorbicacid (vitamin C), vitamin E and glutathione, and stable derivativesthereof, and mixtures thereof; to relieve oxidative stress on the woundbed;

metal ion chelators and/or ion exchangers, such as transition metal ionchelators, such as iron III chelators (Fe III is involved in oxidativestress on the wound bed.), such as desferrioxamine (DFO),3-hydroxytyramine (dopamine); iron III reductants;protease inhibitors, such as TIMPs and alpha 1-antitrypsin (AAT); serineprotease inhibitors, such as 4-(2-aminoethyl)-benzene sulphonyl fluoride(AEBSF, PefaBloc) and N-α-p-tosyl-L-lysine chloro-methyl ketone (TLCK)and ε-aminocaproyl-p-chlorobenzylamide; cysteine protease inhibitors;matrix metalloprotease inhibitors; and carboxyl (acid) proteaseinhibitors;sacrificial redox materials that are potentially or actually beneficialin promoting wound healing, by the removal of materials that trigger theexpression into wound exudate of redox-sensitive genes that aredeleterious to wound healing; autoinducer signalling molecule degraders,which may be enzymes; andanti-inflammatory materials to bind or destroy lipopolysaccharides, e.g.peptidomimetics;agents for the adjustment of pH in the wound exudate, such as base oracid scavengers and/or ion exchangers, or other species, which may benon-labile, insoluble and/or immobilised) species, such as ScavengePore®phenethyl morpholine (Aldrich).

Other physiologically active components of the exudate that aredeleterious to wound healing may be removed in this way.

These may be removed with suitable chelators and/or ion exchangers,degraders, which may be enzymes, or other species.

The following types of functionalised substrate has sites on its surfacethat are capable of removing materials deleterious to wound healing onpassing the circulating fluid from the wound over them:

heterogeneous resins, for example silica-supported reagents such as:metal scavengers,

-   3-(diethylenetriamino)propyl-functionalised silica gel-   2-(4-(ethylenediamino)benzene)ethyl-functionalised silica gel-   3-(mercapto)propyl-functionalised silica gel-   3-(1-thioureido)propyl-functionalised silica gel-   triamine tetraacetate-functionalised silica gel    or electrophilic scavengers,-   4-carboxybutyl-functionalised silica gel-   4-ethyl benzenesulfonyl chloride-functionalised silica gel propionyl    chloride functionalised silica gel-   3-(isocyano)propyl-functionalised silica gel-   3-(thiocyano)propyl-functionalised silica gel-   3-(2-succinic anhydride)propyl-functionalised silica gel-   3-(maleimido)propyl-functionalised silica gel    or nucleophilic scavengers,-   3-aminopropyl-functionalised silica gel-   3-(ethylenediamino)-functionalised silica gel-   2-(4-(ethylenediamino)propyl-functionalised silica gel-   3-(diethylenetriamino)propyl-functionalised silica gel-   4-ethyl-benzenesulfonamide-functionalised silica gel-   2-(4-toluenesulfonyl hydrazino)ethyl-functionalised silica gel-   3-(mercapto)propyl-functionalised silica gel-   dimethylsiloxy-functionalised silica gel    or base or acid scavengers,-   3-(dimethylamino)propyl-functionalised silica gel-   3-(1,3,4,6,7,8-hexahydro-2H-pyrimido-[1,2-a]pyrimidino)propyl-functionalised    silica gel-   3-(1-imidazol-1-yl)propyl-functionalised silica gel-   3-(1-morpholino)propyl-functionalised silica gel-   3-(1-piperazino)propyl-functionalised silica gel-   3-(1-piperidino)propyl-functionalised silica gel-   3-(4,4′-trimethyldipiperidino)propyl-functionalised silica gel-   2-(2-pyridyl)ethyl-functionalised silica gel-   3-(trimethylammonium)propyl-functionalised silica gel or the    reagents,-   3-(1-cyclohexylcarbodiimido)propyl-functionalised silica gel    TEMPO-functionalised silica gel-   2-(diphenylphosphino)ethyl-functionalised silica gel-   2-(3,4-cyclohexyldiol)propyl-functionalised silica gel-   3-(glycidoxy)propyl-functionalised silica gel-   2-(3,4-epoxycyclohexyl)propyl-functionalised silica gel-   1-(allyl)methyl-functionalised silica gel-   4-bromopropyl-functionalised silica gel-   4-bromophenyl-functionalised silica gel-   3-chloropropyl-functionalised silica gel-   4-benzyl chloride-functionalised silica gel-   2-(carbomethoxy)propyl-functionalised silica gel-   3-(4-nitrobenzamido)propyl-functionalised silica gel-   3-(ureido)propyl-functionalised silica gel    or any combinations of the above.

The use of such captive (non-labile, insoluble and/or immobilised)species, such as the foregoing, bound to an insoluble and immobilised)substrate over and/or through which the irrigant and/or wound exudatefrom, the wound dressing passes has been described hereinbefore assuitable for the means for fluid cleansing.

However, they may additionally, where appropriate, be used in any partof the apparatus that is in contact with the irrigant and/or woundexudate, but often within the dressing, for removal of materialsdeleterious to wound healing from wound.

In a second aspect of the present invention there is provided a methodof treating wounds to promote wound healing using the apparatus forcleansing wounds of the present invention.

The present invention will now be described by way of example only withreference to the accompanying drawings in which:

FIGS. 1 to 15 are cross-sectional views of apparatus for cleansing awound according to the first aspect of the present invention.

FIGS. 1 to 11 and 14 show apparatus with a single-phase means for woundexudate cleansing, and of these:

FIGS. 1, 2, 3, 6 7 and 14 show a reversing system, in which the woundexudate and optionally irrigant passes through the cleansing means oneor more times at least once in opposing directions; and

FIGS. 2, 4, 5, 8, 9, 11 and 15 show a circulating system, in whichit/they pass in only one direction; and

FIGS. 12 and 13 show apparatus with a two-phase means for wound exudatecleansing, and of these:

FIGS. 12 and 13 show such apparatus in which the cleansing phase passesthrough the cleansing means.

Referring to FIGS. 1 to 10 and 14, the apparatus (1) for cleansingwounds comprises

a conformable wound dressing (2), havinga backing layer (3) which is capable of forming a relatively fluid-tightseal or closure over a wound and bears an adhesive film, to attach it tothe skin sufficiently to hold the wound dressing (2) in place;a cleansing means (4) for selectively removing materials that aredeleterious to wound healing from wound exudate, which means is underthe backing layer (3) and sits in the underlying wound in use; anda moving device (7) for moving fluid through the cleansing means.

Optional means for bleeding or supplying fluid to the cleansing means(4) or to exudate under the backing layer, e.g. a regulator, such as avalve are omitted in most of the Figures.

In FIG. 1, a reversing system is shown (wound exudate passes through thecleansing means at least once in opposing directions).

The microbe-impermeable film backing layer (3) bears a centrallyattached proximally projecting recessed boss (11).

A porous film (12) and a permeable membrane (13) mounted in the recess(14) of the boss (11) define a cleansing chamber (15), which contains asolid particulate (not shown) for sequestering deleterious materialsfrom, but initially separated from the wound exudate. These integersform the cleansing means (4).

An annular chamber (16) about the boss (11) is defined by afluid-impermeable film (17) that extends between and is attached to theboss (11) and the underside of the backing layer (3). It is filled witha flexibly resilient foam (18)

An inlet and outlet pipe (19) passes centrally through the boss (11) andcommunicates between the interior of the boss (11) and a syringe barrel(20), which is part of a syringe moving device (7).

In use, movement of the syringe plunger (22) sucks and forces woundexudate to and fro through the cleansing means (4).

The apparatus (1) in FIG. 2 may be operated as a circulating system oras both a circulating system and as a reversing system.

It is similar in construction to FIG. 1, but differs mainly in that aninlet pipe return loop (19) passes in a bend through the boss (11) andcommunicates between the interior of the chamber (16) and the syringebarrel (20) via a non-return valve (21), the resistance of which to flowis low relative to the resistance of the cleansing means (4). Means forbleeding fluid from the chamber (16), such as a valve, is omitted fromFIG. 2.

In use, the plunger (22) of the syringe moving device (7) is withdrawnto suck wound exudate into the cleansing means (4), which sequestersdeleterious materials from the wound exudate.

The plunger (22) of the syringe moving device (7) is then returned toforce cleansed wound exudate through the valve (21) into the annularchamber (16), and thence through the porous film (17) back into thewound.

A proportion of cleansed wound exudate is also pushed back through thecleansing means (4) at each return stroke of the syringe plunger. Theproportion will depend largely on the position of the return loop (19)on the syringe barrel. The amount pumped to the annular chamber (16)will decrease the further from the proximal end of the syringe thereturn loop links to the syringe barrel, as the plunger cuts off thereturn loop (19) in the later part of the return stroke.

Depending largely on the type of cleansing means that is employed inthis embodiment of the apparatus of the present invention, theresistance of the valve (21) relative to the resistance of the cleansingmeans (4) may also affect the proportion through the chamber (16) andthrough the porous film (17).

Excess pressure in the chamber (16), e.g. from wound exudate from awound in a highly exuding state, may be relieved by a bleed valve, iffitted.

The apparatus (1) in FIG. 3 differs mainly from that in FIG. 2 in theposition of the porous film (12) in the flow path.

The mode of use is the same: movement of the syringe plunger (22) sucksand forces wound exudate to and from through the cleansing means (4).

The apparatus (1) in FIG. 4 differs from that in FIG. 2 in the movingdevice (7).

This is a press-button pump in place of a syringe. The pump (7) ismounted on the distal face of the backing layer (3).

It comprises a resiliently compressible intake chamber (26), connectedby an outlet pipe (19) to the cleansing means (4) and by a transfer tube(27) via a low resistance first non-return valve (31) to a resilientlycompressible output chamber (36), connected via an inlet pipe (20) and alow resistance second non-return valve (32) to the interior of thechamber (16).

In use, the intake chamber (26) is manually compressed and released, itsreturn to its original configuration causing wound exudate to be drawnthrough the cleansing means (4).

The output chamber (36) is then manually compressed and released, itsreturn to its original configuration causing cleansed wound exudate tobe drawn through the first non-return valve (31) from the intake chamber(26).

The intake chamber (26) is then manually compressed again and released,its compression causing cleansed wound exudate to be pumped into theoutput chamber (36) through the first non-return valve (31) from theintake chamber (26), and its return to its original configurationcausing wound exudate to be drawn through the cleansing means (4).

The output chamber (36) is then manually compressed again and released,its compression causing cleansed wound exudate to be pumped into thechamber (16) through the second non-return valve (32) from the outputchamber (36), and its return to its original configuration causingcleansed wound exudate to be drawn through the intake chamber (26).

The cycle is repeated as long as desired, and from the second cycleonwards, when the output chamber (36) is manually compressed, it causescleansed wound exudate to be forced through the annular chamber (16),and thence through the porous film (17) back into the wound.

Referring to FIGS. 5 to 7 and 10, the apparatus (1) in each comprises acleansing means (4), which comprises a chamber (5), here a conformablehollow bag, defined by the backing layer (3) and a polymer film (6) thatis permeable and permanently attached to the proximal face of thebacking layer (3).

It sits under the domed backing layer (3) in the underlying wound inuse, and contains a cleansing fluid absorbed in a resiliently flexiblefoam (41).

FIGS. 5 to 7 and 10 show different methods of moving wound exudate inand out of the cleansing means (4).

In FIG. 5, an electromechanical oscillator or piezoelectric transducer(43) is mounted centrally in contact with the backing layer (3) on arigid frame (44) mounted at the periphery of the backing layer (3), andis connected electrically to an appropriate alternating electrical powersource (45) (shown schematically). The chamber (5) is provided with ableed valve (8).

If exudate build up under the backing layer (3) becomes excessive duringuse, the bleed valve (8) may be opened and excess fluid vented off, andany excess pressure relieved.

In FIG. 6, the foam (41) has a resiliently flexible, balloon core (47),which is inflatable and deflatable with a fluid, such as a gas, e.g. airor nitrogen, or a liquid, such as water or saline, to apply varyingpressure to the chamber (5) via an inlet and outlet pipe (48) mounted atthe periphery of the backing layer (3).

The pipe (48) is connected to a suitable moving device (58) (not shown)for moving the inflating fluid in and out of the core (47) and thus tomove wound exudate in and out of the cleansing means (4). Such a deviceis suitably one that is capable of optionally pulsed, reversible fluidmovement.

It may in particular be a small peristaltic pump or diaphragm pump, e.g.preferably a battery-driven miniature portable diaphragm or peristalticpump, e.g. mounted centrally on the backing layer (3) above the chamber(5) and is releasably attached to the backing layer (3).

FIG. 7 shows a variant of the apparatus (1) of FIG. 6. The resilientlyflexible, balloon core (47) under the backing layer (3) is replaced by aresiliently flexible, balloon chamber (49), defined by the backing layer(3) and a rigid polymer dome (50) that is impermeable and permanentlyattached to the distal face of the backing layer (3).

The balloon chamber (49), defined by the backing layer (3) and the rigidpolymer dome (50) is also inflatable and deflatable with a fluid, suchas a gas, e.g. air or nitrogen, or a liquid, such as water or saline, toapply varying pressure to the chamber (5) via an inlet and outlet pipe(51) mounted at the periphery of the backing dome (50).

A suitable moving device (58) (not shown) is used for moving theinflating fluid in and out of the balloon chamber (49) and thus to movewound exudate in and out of the cleansing means (4), as noted in respectof FIG. 6, and may be mounted on the dome (50) rather than the backinglayer (3).

In FIG. 10, an electromagnetic solenoid core (53) within an electricalcoil (54) is mounted centrally in contact with the backing layer (3) ona rigid flange (55). The electrical coil (54) is connected electricallyto an appropriate alternating electrical power source (60) (shownschematically).

The chamber (5) is provided at its base with an attached disc (56) of aferromagnetic material sheathed from the wound exudate and cleansingfluid.

As the direction of current flow alternates, the solenoid core follows,and so compresses and releases the chamber (5), and hence causes woundexudate to be forced to and fro through the cleansing means (4).

FIGS. 8 and 9 show a variant of the apparatus (1) of FIGS. 1 and 4. Themoving device (7) in both cases that respectively replaces the syringeand the press-button pump is a small peristaltic pump or diaphragm pump.

It is preferably a battery-driven miniature portable diaphragm orperistaltic pump, e.g. mounted centrally on the backing layer (3) abovethe chamber (5) and is releasably attached to the backing layer (3).

FIG. 11 shows apparatus with a single-phase means for wound exudatecleansing in which the wound exudate passes through the cleansing meansone or more times in only one direction. It is similar in structure tothe apparatus shown in FIGS. 5 to 7 and 10.

The apparatus (1) comprises a cleansing means (4), which comprises achamber (5), here a conformable hollow bag, defined by the backing layer(3) and a polymer film (6) that is permeable and permanently attached tothe proximal face of the backing layer (3). It contains a cleansingfluid absorbed in a resiliently flexible foam (41).

The resiliently flexible foam (41) is contained in a permeable membrane(43) and contains a material for sequestering deleterious materials fromthe wound exudate.

These integers form the cleansing means (4).

An outlet pipe (69) passes centrally through the backing layer (3) andcommunicates between the interior of the chamber (5) and a pump, e.g.preferably a battery-driven miniature portable diaphragm or peristalticpump, e.g. mounted centrally on the backing layer (3) above the chamber(5) and releasably attached to the backing layer (3).

An inlet pipe (20) passes peripherally through the backing layer (3) andcommunicates between the wound space and the pump.

In use, wound exudate is moved by the pump (7) through the cleansingmeans (4), and the foam (41) sequesters deleterious materials from thewound exudate.

FIG. 12 shows apparatus with a two-phase means for wound exudatecleansing in which the cleansing phase moves.

FIG. 12 a shows apparatus in which the only the cleansing phase moves.

FIG. 12 b shows apparatus in which the cleansing phase and the woundexudate phase move.

In both Figures, the apparatus (1) comprises a cleansing means (4),which comprises a chamber (5), here in the form of tubules in an arrayunder the backing layer (3) between a first boss (71) and a second boss(72) both mounted in the backing layer (3). The tubules are made from apolymer membrane that is selectively permeable to deleterious materialsin the wound exudate, and contain a dialysate fluid.

An inlet pipe (20) passes from the first boss (71) and communicatesbetween the interior of the chamber (5) and a pump (7), e.g. preferablya battery-driven miniature portable diaphragm or peristaltic pump, e.g.mounted centrally on the backing layer (3) above the chamber (5) andreleasably attached to the backing layer (3). An outlet pipe (21) passesfrom the second boss (72) and communicates between the interior of thechamber (5) and the pump (7).

In use, dialysate fluid is moved by the pump (7) through the cleansingmeans (4), and it removes deleterious materials from the wound exudate.

In FIG. 12 b, a third boss (78) with a wound exudate outlet passingcentrally through it and a fourth boss (79) with a wound exudate inletpassing centrally through it are both mounted peripherally and mutuallydiametrically opposed in the backing layer (3).

A wound exudate outlet tube (80) is connected to the third boss (78) andcommunicates between the interior of the wound and the inlet of a secondpump (82) (not shown), e.g. preferably a battery-driven miniatureportable diaphragm or peristaltic pump, mounted centrally on the backinglayer (3).

A wound exudate inlet tube (81) is connected to the fourth boss (79) andcommunicates between the interior of the wound and the outlet of thesecond pump.

In use, not only is dialysate fluid moved by the first pump (7) throughthe cleansing means (4), where it removes deleterious materials from thewound exudate, but the wound exudate phase is moved under the backinglayer (3) through the wound space by the second pump in acounter-current direction to enhance the removal from the wound exudate.

FIG. 13 shows apparatus with a two-phase means for wound exudatecleansing in which the cleansing phase moves.

The apparatus (1) comprises a cleansing means (4), which comprises achamber (5), here in the form of bag under the backing layer (3) andunder a foam filler (81).

This bag is made from a polymer membrane and contains a dialysate fluid,which contains a material as a solute or disperse phase species that isfor sequestering or degrading deleterious materials from the woundexudate. The membrane is chosen to be selectively permeable to allowperfusion of deleterious material species targeted for sequestration ordestruction from the wound exudate into the dialysate, but not to allowany significant amounts of antagonist in the dialysate fluid phase todiffuse freely out of the dialysate into the wound fluid.

An outlet pipe (89) passes through the backing layer (3) andcommunicates between the interior of the chamber (5) and a pump, e.g.preferably a battery-driven miniature portable diaphragm or peristalticpump, e.g. mounted centrally on the backing layer (3) above the chamber(5) and releasably attached to the backing layer (3). An inlet pipe (90)passes peripherally through the backing layer (3) and communicatesbetween the chamber (5) and the pump.

In use, dialysate is moved by the pump (7) through the cleansing means(4). Deleterious material species targeted for sequestration ordestruction from the wound exudate into the dialysate, where theantagonist in the dialysate fluid phase removes deleterious materialsfrom the wound exudate, without diffusing out into the exudate.

In FIG. 14, a reversing system is shown (wound exudate passes throughthe cleansing means at least once in opposing directions) that issimilar in structure to the apparatus shown in FIGS. 1 and 3.

The microbe-impermeable polyurethane film backing layer (3), formed bysolution casting or extrusion, bears a centrally attached proximallyprojecting boss (11) with a luer for connection to a mating end of afluid supply and offtake tube (19), which communicates between theinterior of the boss (11) and a syringe barrel (20), which is part of asyringe moving device (7).

A lower porous film (12) and an intermediate porous membrane (13), bothmade of permeable polyurethane membrane with small apertures or pores,define a cleansing chamber (15), which contains a solid particulate (notshown).

This is for sequestering deleterious materials from, but initiallyseparated from, the wound exudate. These integers, with a coextensiveimpermeable upper sheet (24) with an upper aperture adapted to registerwith the conduit in the boss (11), form an upper chamber (25), and alltogether form the cleansing means (4). This is mounted on the lower faceof the boss (11) with the upper aperture in register with the conduit inthe boss (11).

In use, movement of the syringe plunger (22) sucks and forces woundexudate to and fro through the cleansing means (4).

The apparatus (1) in FIG. 15 is a circulating system (wound exudatepasses through the cleansing means one or more times in only onedirection). It is a variant of the apparatus (1) of FIGS. 8 and 9.

The microbe-impermeable polyurethane film backing layer (3), formed bysolution casting, bears a centrally mounted proximally projecting boss(11) with a uniform cylindrical-bore conduit through it and a luer forconnection to a mating end of a fluid supply tube (20), whichcommunicates between the interior of the boss (11) and the outlet ofmoving device (7).

The moving device (7) is a battery-driven miniature portable diaphragmor peristaltic pump, mounted centrally on the backing layer (3) and isreleasably attached to the backing layer (3).

A second proximally projecting boss (82) with a luer for connection to amating end of a fluid offtake tube (83) is mounted peripherally on thebacking layer (3). The fluid offtake tube (83) communicates between thewound space and the inlet of the pump (7).

A lower porous film (12) and an intermediate porous membrane (13), bothmade of permeable polyurethane membrane with small apertures or pores,define a cleansing chamber (15), which contains a solid particulate (notshown) for sequestering deleterious materials from, but initiallyseparated from, the wound exudate. These integers, with a coextensiveimpermeable upper sheet (24) with an upper aperture adapted to registerwith the conduit in the boss (11), form an upper chamber (25), and alltogether form the cleansing means (4).

This is mounted on the lower face of the boss (11) with the upperaperture in register with the conduit in the boss (11).

In use, wound exudate is moved by the pump (7) through the cleansingmeans (4), and the particulate (not shown) sequesters deleteriousmaterials from the wound exudate

The use of the apparatus of the present invention will now be describedby way of example only in the following Examples:

EXAMPLE 1 Cleansing Fe(II) from Aqueous Solution with the Apparatus ofFIG. 1: Single-Phase Hand-Syringe Pumped Dressing Containing SolidSequestrant (Cadexomer-Desferrioxamine)

A hand-syringe pumped dressing as shown in FIG. 14 was made up. Thecleansing chamber (15) contains a solid particulate (not shown)desferrioxamine supported on Cadexomer (50 mg) to sequester and removedeleterious Fe(II) ions from surrogate exudate.

The porous film (12) and a permeable membrane (13), both made of Porvairpermeable membrane, are chosen to allow perfusion and flow under syringepumping through the cleanser but to contain the solid reagent.

In triplicate, the dressing as shown in FIG. 1 was applied to a 9.60 mlcapacity circular wound cavity (cast in Perspex) containing an aqueoussolution of ferrous chloride tetrahydrate (Aldrich) (9.60 ml, 200μmolar).

The solution was repeatedly completely withdrawn and completelyreinjected using the device syringe. At each withdrawal, a 100microlitre aliquot of solution was assayed using a ferrozine assay asfollows: each 100 ul aliquot was added immediately to a 1.5 ml capacity,1 cm path-length UV cuvette containing 1 ml Ferrozine stock solution(73.93 mg Ferrozine was made up to 250 ml in distilled water (600 uM)).Absorbance (562 nm) readings were taken after at least 5 min.incubation. The absorbance was measured using UNICAM UV4-100 UV-Visspectrophotometer V3.32 (serial no. 022405).

Six passes were made in total, at four minute intervals. The same methodwas repeated in the absence of flow (i.e. without syringe pumpingthrough the cleanser) and sampled at equivalent time points.

Results and Conclusions

The resulting iron concentration profiles were averaged and the standarddeviations were determined. The Fe(II) concentration is effectivelydepleted to background level in 3 full cycles (12 minutes). In thecontrol, insignificant concentration change has occurred in the sametime period.

The dressing as shown in FIG. 1 effectively sequesters Fe(II) fromaqueous solution such as water, saline or wound exudate.

EXAMPLE 2 Neutralising the pH of an Acidic Solution with the Apparatusof FIG. 15: Single-Phase Recirculating Pumped Dressing Containing SolidAcid Scavenger, ScavengePore® Phenethyl Morpholine

A recirculating pumped dressing as shown in FIG. 15 was made up. Thecleansing chamber (15) contains a solid particulate (not shown) ofScavengePore® phenethyl morpholine (Aldrich) (50 mg), which is alow-swelling macroporous highly crosslinked polystyrene/divinylbenzeneion-exchanger resin matrix, with 200-400 micron particle size, toscavenge and remove protons, which are acidic species which adverselyaffect the pH in the wound exudate, from surrogate exudate.

The porous film (12) and a permeable membrane (13), both made of Porvairpermeable membrane, are chosen to allow perfusion and flow under pumpingthrough the cleanser but to contain the ion-exchange reagent.

In triplicate, 4.80 ml DMEM was In triplicate, Device 2 was applied to a9.60 ml capacity circular wound cavity (cast in Perspex) containingDulbecco's Modified Eagles Medium (DMEM) (Sigma) (4.80 ml, pH adjustedto pH 6.6 using hydrochloric acid (0.975 N in water, 75 μl). Theremaining cavity volume was filled with glass beads. The solution wascirculated through the cavity at a flow rate of 2.35 ml min⁻¹.

100 μl samples were taken at 5 min. time points up to 40 min, and pH wasrecorded using a flat-bed pH meter. The same method was repeated in theabsence of flow (i.e. no pump circulation of the solution) and sampledat equivalent time points.

Results and Conclusions

The resulting pH profiles were averaged and standard deviationsdetermined. The pH was effectively adjusted to pH 7.4 in 40 min. In thecontrol, a slower change in pH was observed in the same time period topH 7.

EXAMPLE 3 Cleansing Elastase from Aqueous Solution by Diffusion Across aDialysis Membrane with the Apparatus of FIG. 12: Two-Phase RecirculatingPumped Dressing Containing No Reagent

A recirculating pumped dressing as shown in FIG. 12 was made up. Thecleansing chamber (5) is in the form of tubules made from a polymermembrane that is selectively permeable to a deleterious materials inwound exudate (elastase). These in an array under the backing layer (3)within the wound space between a first boss (71) and a second boss (72)both mounted in the backing layer (3). The tubules contain a dialysatefluid and are in a circuit with a pump (7).

In triplicate, the dressing as shown in FIG. 12 was applied to a 9.60 mlcapacity circular wound cavity (cast in Perspex) containing elastasesolution (porcine pancreatic elastase, Sigma) (4.80 ml, 0.5 mgml⁻¹ inTRIS buffer, pH 8.2, 0.2 M). The remaining cavity volume was filled withglass beads. The inlet and outlet ports were connected to thecirculating pump.

The dialysate system was prefilled with TRIS (pH 8.0, 0.2 M). This wascirculated through the dressing at a flow rate of 2.35 ml min⁻¹. 10 μlsamples of the circulating solution were taken at 5 min. time points upto 45 min, and the activity was recorded using a standardN-succinyl-(ala)₃-p-nitroanilide colorimetric assay. The same method wasrepeated in the absence of flow (i.e. no pump circulation of thesolution) and sampled at equivalent time points.

Results and Conclusions

The activity of the samples was determined from their absorbances at 405nm using a UV/Vis spectrometer. Results were averaged and standarddeviations determined. Effective transfer of elastase across thedialysis membrane is seen in 45 min. In the control, no effectivetransfer was observed in the same time period.

EXAMPLE 4 Cleansing Fe(II) from Aqueous Solution with the Apparatus ofFIG. 13: Two-Phase Recirculating Pumped Dressing Containing Liquid PhaseSequestrant (Starch-Desferrioxamine (DFO) Conjugate)

An analogue of the apparatus (1) in FIG. 13 was made up, i.e. with acirculating system (wound exudate passes through the cleansing means oneor more times in only one direction) with a two-phase means for woundexudate cleansing in which the cleansing phase moves.

The apparatus (1) comprises a cleansing means (4), which comprises achamber (5) which is made from a polymer membrane and contains adialysate fluid, which contains a material as a solute or disperse phasespecies that is for sequestering or degrading deleterious materials fromthe wound exudate.

The membrane is chosen to be selectively permeable to allow perfusion ofdeleterious material species targeted for sequestration or destructionfrom the wound exudate into the dialysate, but not to allow anysignificant amounts of antagonist in the dialysate fluid phase todiffuse freely out of the dialysate into the wound fluid.

The analogue is a circuit containing a 0.5-1.0 ml capacity Slide-A-Lyzerdialysis unit, with an upper chamber and a lower chamber in which woundexudate and cleansing fluid respectively are separated from each otherby a polymer membrane chosen to have the properties noted above (MWCO10000).

The lower chamber, through which cleansing fluid passes, has diagonallyopposed inlet and outlet ports, which are opened with needles, connectedto a circuit of 5 ml capacity containing a dialysate reservoir and abattery-driven miniature portable diaphragm or peristaltic pump. Thecircuit contains an aqueous high molecular weight starch—DFO conjugate(5 ml, 4 mg/ml).

An aliquot of ferrous chloride tetrahydrate (Aldrich) solution (0.5 ml 3mM) was placed in the upper cavity of the slide and dialysed with 3.6ml/min. flow in the circuit and (as a control) in the absence of flow inthe circuit.

10 microlitre aliquots were removed for 30 minutes at 5 minutesintervals (including t=0). The 10 microlitre aliquot of solution wasassayed using the ferrozine iron(II) determination assay as described inExample 1 above. These experiments were performed in triplicate.

Results and Conclusions

The resulting iron concentration profiles were averaged and standarddeviations determined. The Fe(II) concentration was effectively depletedto approximately 50% of the initial level in 30 minutes. Without circuitflow, Fe(II) concentration was depleted to approximately 75% of thestarting value in the same time period. The apparatus effectivelysequesters Fe(II) from aqueous solution.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.A wound therapy device, comprising: a backing layer to cover at least aportion of a wound site; a chamber under the backing layer, wherein thechamber is configured to retain and store wound exudate from the woundsite upon application of negative pressure; an outlet for communicatingwith a vacuum source and for supplying negative pressure to the woundand to the chamber; and a porous member configured to retain woundexudate in the chamber.
 12. The wound therapy device of claim 11,wherein the backing layer forms a seal over the wound.
 13. The woundtherapy device of claim 11, wherein the backing layer is sufficientlyrigid to resist deformation under pressure in any direction.
 14. Thewound therapy device of claim 11, wherein the backing layer material ischosen from polyolefins, polyethylenes, polypropylenes, vinyl acetates,polyvinyl alcohols, polysiloxanes, polyesters, polycarbonates,polyamides, polyurethanes, polystyrenes, copolymers thereof, andmixtures thereof.
 15. The wound therapy device of claim 11, wherein thebacking layer is flexible.
 16. The wound therapy device of claim 11,further comprising at least one support for supporting and strengtheningthe backing layer.
 17. The wound therapy device of claim 16, wherein thesupport comprises a flange.
 18. The wound therapy device of claim 11,further comprising foam underneath the backing layer.
 19. The woundtherapy device of claim 11, wherein the porous member comprises amicropore filter.
 20. The wound therapy device of claim 11, wherein theporous member comprises a polymeric membrane.
 21. The wound therapydevice of claim 11, wherein the porous member comprises a hydrophobicmaterial selected from the group consisting of polyesters,polycarbonates, PTFE, polyamides, hydrophobic polyurethanes, and quartzand glass fibres.
 22. The wound therapy device of claim 11, wherein thechamber comprises a porous filler.
 23. The wound therapy device of claim22, wherein the porous filler is selected from the group consisting of:foams, gels, and solid particulates.
 24. The wound therapy device ofclaim 11, wherein the chamber further comprises an inhibitor ofmicrobial growth.
 25. The wound therapy device of claim 11, wherein theoutlet comprises a connector for connecting to a fluid moving device.26. The wound therapy device of claim 11, wherein the outlet is coupledto a miniature pump.
 27. The wound therapy device of claim 11, furthercomprising a bleed valve to relieve excess pressure.
 28. The woundtherapy device of claim 11, wherein the negative pressure is regulatedby a control device.
 29. The wound therapy device of claim 11, whereinthe backing layer is constructed of plastic selected from the groupconsisting of: polypropylene, polyurethane, polyethylene, polyesters,polyamides, polysiloxanes, and copolymers and mixtures thereof.
 30. Thewound therapy device of claim 11, further comprising a permeable film.31. The wound therapy device of claim 30, wherein the permeable film isconfigured to contact the wound.
 32. The wound therapy device of claim30, wherein the permeable film is attached to the skin around the wound.33. The wound therapy device of claim 30, wherein the permeable filmcomprises a high moisture vapor permeability material.
 34. The woundtherapy device of claim 11, wherein the backing layer is constructedfrom a high moisture vapor permeability material.